Photocell controlled LED driver circuit

Abstract

An illustrative LED driver circuit includes an automatic on and off control function using a light sensing circuit having a light sensing element reacting to ambient light. The circuit uses flyback converter topology and a power factor correction (PFC) controller. The light sensing function is provided by coupling the light sensing circuit to a monitoring/disable function of the PFC controller, thus providing automatic on and off control of the LED driver circuit by using a light sensing element such as a photocell.

The invention claimed is: 
     
       1. An LED driver circuit with automatic on and off ambient light control, comprising:
 a power factor correction controller, the controller including a monitor input that enables/disables an output of the LED driver circuit; and 
 a light sensing circuit including a light sensing element and a voltage divider, an output of the light sensing circuit changing based on the light sensing element responding to changes in ambient light, the output of the light sensing circuit coupled to the monitor input of the controller; and 
 wherein the output of LED driver circuit is enabled/disabled in response to the changes in ambient light. 
 
     
     
       2. The LED driver circuit of  claim 1 , wherein the light sensing element includes a photocell. 
     
     
       3. The LED driver circuit of  claim 1 , further comprising a flyback converter, and where the output of the LED driver circuit is provided by the flyback converter. 
     
     
       4. An LED driver circuit with automatic on and off ambient light control, comprising:
 a power factor correction controller, the controller including a monitor input that enables/disables an output of the LED driver circuit; and 
 a light sensing circuit including a light sensing element, an output of the light sensing circuit changing based on the light sensing element responding to changes in ambient light, the output of the light sensing circuit coupled to the monitor input of the controller; and 
 wherein the output of the LED driver circuit is enabled/disabled in response to the changes in ambient light; 
 wherein the light sensing circuit further comprises a first resistor and a first capacitor in parallel and defining a first and second node, the light sensing element coupled to the first node and an opposite terminal defining a third node, the second node coupled to a ground, the third node coupled to a voltage supply, and the first node defining the output of the light sensing circuit. 
 
     
     
       5. An LED driver circuit with automatic on and off ambient light control, comprising;
 a power factor correction controller, the controller including a monitor input that enables/disables an output of the LED driver circuit; and 
 a light sensing circuit including a light sensing element, an output of the light sensing circuit changing based on the light sensing element responding to changes in ambient light, the output of the light sensing circuit coupled to the monitor input of the controller; and 
 wherein the output of the LED driver circuit is enabled/disabled in response to the changes in ambient light; 
 wherein the light sensing circuit further comprises a first and second resistor, a first capacitor, and a first transistor, the first resistor and first capacitor in parallel and defining a first and second node, the light sensing element coupled to the first node and an opposite terminal defining a third node, the transistor having a base, emitter, and collector, the base coupled to the first node, the emitter coupled to the second node, the collector forming a fourth node, the second resistor coupled between the fourth node and the third node, the second node coupled to a ground, the third node coupled to a voltage supply, and the fourth node defining the output of the light sensing circuit. 
 
     
     
       6. An LED driver circuit with automatic on and off ambient light control, comprising:
 a power factor correction controller, the controller including a monitor input that enables/disables an output of the LED driver circuit; and 
 a light sensing circuit including a light sensing element, an output of the light sensing circuit changing based on the light sensing element responding to changes in ambient light, the output of the light sensing circuit coupled to the monitor input of the controller; and 
 wherein the output of the LED driver circuit is enabled/disabled in response to the changes in ambient light; 
 wherein the light sensing circuit further comprises a first, second, and third resistor, a first capacitor, and a first operational amplifier, the first resistor and first capacitor in parallel and defining a first and second node, the light sensing element coupled to the first node and an opposite terminal defining a third node, the operational amplifier having an output, an inverting input, and a non-inverting input, the inverting input coupled to the first node, the non-inverting input defining a fourth node, the second resistor coupled between the fourth node and the third node, the third resistor coupled between the fourth node and the second node, the second node coupled to a ground, the third node coupled to a voltage supply, and the output of the operational amplifier defining the output of the light sensing circuit. 
 
     
     
       7. An LED driver circuit with automatic on and off ambient light control, comprising:
 a power factor correction controller, the controller including a monitor input that enables/disables an output of the LED driver circuit; and 
 a light sensing circuit including a light sensing element, an output of the light sensing circuit changing based on the light sensing element responding to changes in ambient light, the output of the light sensing circuit coupled to the monitor input of the controller; and 
 wherein the output of the LED driver circuit is enabled/disabled in response to the changes in ambient light; 
 wherein the light sensing circuit further comprises a first, second, third, and fourth resistor, a first capacitor, and a first operational amplifier, the first resistor and first capacitor in parallel and defining a first and second node, the light sensing element and the fourth resistor in parallel and coupled to the first node and an opposite terminal defining a third node, the operational amplifier having an output, an inverting input, and a non-inverting input, the inverting input coupled to the first node, the non-inverting input defining a fourth node, the second resistor coupled between the fourth node and the third node, the third resistor coupled between the fourth node and the second node, the second node coupled to a ground, the third node coupled to a voltage supply, and the output of the operational amplifier defining the output of the light sensing circuit.